I just recently upgraded to version 10.13.6 on my Mac Mini and now Myth Backend won't start. It has been running flawlessly for a couple of years without any issues. I am using the previous macports installer by craig.

BTW, have you waited 10 minutes? For a lot of people, on a fresh reboot, mythbackend fails to start the first time it tries to launch as something (networking?) isn't ready. The OS will automatically try again within 10 minutes and, for most people affected, away it goes.